1. Field of the Invention
The present invention relates to a speed detecting apparatus which is applied, for example, to an electronic keyboard musical instrument such as an electronic piano, and a composite piano such as a silent piano and an automatically playing piano for detecting the speed of pivotal movements of a key or a hammer.
2. Description of the Prior Art
Generally, when an electronic piano is played or when a silent piano is played in silence, a detection is generally made for a speed at which a key or a hammer pivotally moves in association with a touch on the key, a velocity is determined based on the detected pivot speed, and a volume to be generated is determined based on the determined velocity. This is because the volume of an acoustic piano and the like is determined in accordance with a speed at which a key is touched, a speed at which a hammer strikes a string, and the like.
In the past, Laid-open Japanese Patent Application No. 02-160292, for example, discloses a speed detecting apparatus for detecting a pivot speed of a hammer. As illustrated in FIG. 1, the disclosed speed detecting apparatus 61 comprises a pivotable key (not shown), a hammer 63 pivotably supported by a center pin 68 to pivotally move in association with a touch on the key to strike a string 62, a shutter 64 arranged on the hammer 63, a first to a third sensor 65, 66, 67, and the like. The shutter 64 is formed in a planar fan shape, and is fixed to a catch shank 63a of the hammer 63. The first to third sensors 65-67 are arranged in a straight line with certain intervals defined therebetween. Each of the first to third sensors 65-67 comprises a pair of a light emitter and a light receiver (none of which is shown), and is configured such that light emitted from the light emitter is received by the light receiver. These light emitters and light receivers are arranged on both sides of a shutter moving path, and in a key releasing state (the components are positioned as indicated by solid lines in FIG. 1), the shutter 64 does not overlap with any sensor, but is positioned nearby.
In the structure as described above, a touch on the key causes the hammer 63 to pivotally move about the center pin 68 in the counter-clockwise direction in FIG. 1, associated with the touch. This pivotal movement of the hammer 63 causes the shutter 64 to sequentially block the light from the first to third sensors 65-67, so that the first to third sensors 65-67 generate detection signals in response to the blocking of light emitted therefrom. Among these detection signals, the detection signal from the first sensor 65 is used to detect positional information on the key, while the detection signals from the second and third sensors 66, 67 are used to detect the pivot speed of the hammer 63. Specifically, a time required for the shutter 64 to move between the second sensor 66 and the third sensor 67 is detected based on the timings at which the light is blocked at the second and third sensors 66, 67, respectively, and the pivot speed of the hammer 63 is determined in accordance with the detected moving time.
In this conventional speed detecting apparatus 61, since the hammer 63 pivotally moves about the center pin 68, the shutter 64 integrated with the hammer 63 also moves along an arc centered at the center pin 68. On the other hand, the first to third sensors 65-67 are simply arranged in a straight line, so that if the shutter 64 is attached at a deviated position or angle due to errors in dimensions or assembly of parts, the shutter 64 will block the light from the first to third sensors 65-67 at actual points (hereinafter called the “light blocking points”) which deviate from correct points, causing an associated change in stroke (hereinafter called the “light blocking stroke”) of the hammer 63 actually required to block the light from the next sensor after it has blocked the light from a certain sensor. Since such a change in the light blocking stroke results in a change in the detected moving time of the shutter 64 between the sensors, the pivot speed of the hammer 63, determined on the basis of the moving time of the shutter 64, would be detected with a lower accuracy.
Such a disadvantage can be solved by correcting the position or angle at which the shutter 64 is attached. However, since the shutter 64 is generally driven into or adhered to the catch shank 63a for attachment thereto, great efforts will be exerted to modify the shutter 64 in position or angle of attachment, resulting in an increased manufacturing cost.
Laid-open Japanese Patent Application No. 09-068981, for example, also discloses a speed detecting apparatus for detecting a pivot speed of a key. As illustrated in FIG. 2, the disclosed speed detecting apparatus 71 comprises a pivotable key 72, a shutter 73 integrally arranged on the bottom surface of the key 72, two photo-couplers 74, 75 arranged below the shutter 73, and the like. The shutter 73 extends in the left-to-right and up-to-down directions, and is formed in a rectangular shape. The shutter 73 is formed with an optically transparent window 76. The optically transparent window 76 is formed in an inverted L-shape, made up of a left half 76a which extends over substantially the entirety of the shutter 73 in the vertical direction, and a right half 76b which extends to the right from the upper half of the left half 76a, where the lower end of the right half 76b is higher than the lower end of the left half 76a. The two photo-couplers 74, 75 are arranged side by side adjacent to each other, and comprise a pair of a light emitters 74a and a light receiver 74b, and a pair of a light emitter 75a and a light receiver 75b, respectively. These light emitters 74a, 75a and light receivers 74b, 75b are arranged on both sides of a path along which the shutter 73 moves.
In the structure as described above, as the key 72 is touched, the shutter 73 pivotally moves downward in association with a pivotal movement of the key 72, causing the lower end of the shutter 73 to reach the two photo-couplers 74, 75, thereby blocking light to the respective light receivers 74b, 75b. Next, as the lower end of the left half 76a of the optically transparent window 76 reaches the left-hand photo-coupler 74, light reaches the light receiver 74b of the photo-coupler 74. As the shutter 73 further pivotally moves, the lower end of the right half 76b of the optically transparent window 76 reaches the right-hand photo-coupler 75, permitting light to reach the light receiver 75b of the photo-coupler 75. Each of the photo-couplers 74, 75 generates a detection signal in response to the light reaching the light receiver 74b, 75b or blocked by the shutter 73. A pivot speed of the key 72 is detected in accordance with these detection signals.
Disadvantageously, in the conventional speed detecting apparatus 71 described above, the pivot speed of the key 72 is detected in accordance with the timings at which the single shutter 73 reaches the two photo-couplers 74, 75. As such, if the shutter 73 is obliquely attached as illustrated in FIG. 3, a shift will be brought in a light blocking stroke d between the left and right photo-couplers 74, 75, causing a consequent degradation in accuracy of detecting the pivot speed. While such a problem can be solved by modifying the angle at which the shutter 73 is attached, the modification will require great efforts, resulting in an increase in the manufacturing cost, from the same reason as the aforementioned Laid-open Japanese Patent Application No. 02-160292.